Linear motor with improved coil design and heat removal

ABSTRACT

A linear motor comprising a DC magnetic field of alternating polarity arranged in a longitudinal axis, a coil assembly located substantially in a plane parallel to and immersed in the alternating magnetic field, said coil assembly containing individual coil loops of essentially rectangular shape and having end turn areas arranged parallel to said longitudinal axis of the magnet field and coil side areas being perpendicular to said longitudinal axis of the magnetic field with each coil side having a coil side width (CSW) and each coil loop having a coil outside width (COW) and coil inside width (CIW) such that COW=CIW+(2×CSW) wherein the coils have a coil outside length (COL), forming a coil assembly area (CAA) approximately equal to COW×COL and said coil assembly has a coil assembly thickness (CAT) in a direction creating acoil assembly volume (CAV) approximately equal to the coil assembly area (CAA) times the coil assembly thickness (CAT) pursuant to the following equation: CAV≈CAT×COW×COL. wherein said assembly is formed with a plurality of phases each formed in the manner of the first phase, each phase uniformly and sequentially offset from adjacent phases and means for switching current successively between the phases thereby alternating the magnetic fields within the coil assembly sequentially, said plurality of offset phases substantially filling the coil inside width (CIW) of the first phase, such that CIW=CSW×(#φ-1). The above coil assembly optimally includes a longitudinal opening along the end turn areas within the coil assembly volume allowing non-magnetic metallic members for heat dissipation and structural strength, including a mounting bracket on one end turn area, and a heat sink cap enclosing the opposite end turn area.

This is a continuation of copending application Ser. No. 08/694,617filed on Aug. 13, 1996 pending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to new and improved linear motors,especially those linear motors having moving coils. As described herein,the coils of the present invention provide more effective multi-pole,multi-phase structures for use in a linear motor, and the presentinvention also describes improvements for the dissipation of heat from alinear motor resulting in better performance and/or longevity.

2. Description of the Prior Art

Linear motors which directly produce a linear force in response to anelectric current are known, and the prior art has been previouslyreviewed. For example, U.S. Pat. No. Re 34,674 notes that linear driveshave been used in many areas, including automation and roboticpositioning systems, printers and disk drive units. One type of linearmotor is, e.g. the linear stepper motor, which is similar to a rotarystepper motor. A second type of linear motor is the moving magnet motor.These motors incorporate a fixed wound stator assembly with the loadattached to a moving magnet assembly. Yet another type of linear motoris the moving coil linear motor. These can be either brush or brushlessdesigns having a moving coil passing through an air gap created byeither two rows of permanent magnets and magnetic circuit completionmeans or back iron with one row of permanent magnets and a magneticcircuit completion means using one back iron and one ferromagnetic bar.

However, the moving coil windings in these motors are generally thelimiting factor to the force that can be developed due to heat buildupin the windings. The linear force developed is proportional to thecurrent passing through the windings, the number of turns of wire andthe flux density in the magnetic circuit. Given a constant flux densityand a given number of turns in the windings, force is then proportionalto the current in the windings. At the same time, the power to bedissipated as heat is proportional to the resistance of and current inthe winding and builds at a rate much greater than the increase inforce. This generally results in a current limitation in the coils beingrequired to prevent overheating of the coil assembly.

With regards to the specific linear motor described in U.S. Pat. No. Re.34,674, said motor was defined as having a central row of alternatingpermanent magnets, with multi-phase, multi-pole coil assemblies locatedon both sides of the magnet row. That is, the coil assemblies were saidto be formed of a series of individual coils connected in a multi-phase,multi-pole relationship. Two coil assemblies are described, each coillocated substantially in a plane parallel to a magnet plane on oppositesides of a magnet row. Furthermore, the coil loop thickness was said tobe approximately said individual coil loop total width divided by twotimes the number of phases, and no foreign material, such asferromagnetic laminations or other metallic materials, was located inthe volume of the coil assembly. Finally, a minimum of two coils perphase were described, in which coils of the same phase are in contactwith one another.

Other prior art motor designs and related subject matter has beendisclosed, and reference is made to the following U.S. Patents foradditional background information: U.S. Pat. No. 4,749,921 "Linear MotorWith Non-Magnetic Armature"; U.S. Pat. No. 4,331,896 "Zig-Zag Windings,Winding Machine and Method"; U.S. Pat. No. 4,303,017 "Long Stator LinearMotor Without Iron"; U.S. Pat. No. 4,369,383 "Linear DC Permanent MagnetMotor"; U.S. Pat. No. 4,575,211 "Brushless D.C. Motor" U.S. Pat. No.3,913,045 "Linear Moving Field Inductor For Electromagnetic Pumps,Conveyor Troughs or Agitator Reels for Liquid Metals"; U.S. Pat. No.3,969,644 "Pulse Generator With Asymmetrical Multi-Pole Magnet".

As can therefore be seen from the above, the moving coil windings emergeas a limiting factor to the force that can be developed due to the heatbuildup in the windings. That being the case, there has been along-standing need to develop new and improved coil designs to improvemotor performance, i.e., a linear motor which develops largeaccelerations, static force and speeds, and which does not require largenumbers of expensive magnets, and does not have a coil assembly whichoverheats.

Accordingly, it is a first object of this invention to provide a coilconfiguration which improves the configurations reported in the priorart, and which can be described in part as containing a coil assemblywhich contains at least two phases having one coil loop per phase,comprised of individual coil loops of essentially rectangular shape,with end turn areas arranged parallel to the longitudinal axis of amagnetic field wherein an opening is provided within the volume of thecoil assembly, and wherein one coil side of the 2nd phase is positionedparallel to and between the coil sides of the first phase for thepurpose of improved linear motor performance.

More specifically, and again with reference to the prior art linearmotor designs summarized above, such designs have not been optimized forheat removal as the coil assemblies were generally only air-cooled andhad poor heat sinking of the coil assemblies. That is, the coilsthemselves were not fully distributed to provide maximum transfer ofheat to a heat sink. Furthermore, the prior art has yet to provide acoil configuration wherein an opening within the volume of the coilloops, as noted above, is specifically located in the end turn areas,disposed along the longitudinal axis of the magnetic path, for thepurpose of improving heat dissipation, and for the placement ofthermally conductive non-magnetic material for structural support.

Additionally, while linear motors of the prior art contained magneticcircuit completion means, said completion means itself had not beenstructurally optimized for heat removal, with regards to, as hereindescribed, the use of plates, and plate separating ribs comprising aplurality of air gaps between separating blocks along the magnet trackaxis.

It is also a primary object of the invention to provide a permanentmagnet linear motor which overcomes the disadvantages of the prior artand provides a new and improved coil geometry, including a heat sinkattached to opposite end turn areas, that can be described as a heatsink cap to improve motor performance.

SUMMARY OF THE INVENTION

A linear motor comprising a DC magnetic field of alternating polarityarranged in a longitudinal axis, a coil assembly located substantiallyin a plane parallel to and immersed in the alternating magnetic field,said coil assembly containing individual coil loops of essentiallyrectangular shape and having end turn areas arranged parallel to saidlongitudinal axis of the magnetic field and coil side areas beingperpendicular to said longitudinal axis of the magnetic field with eachcoil side having a coil side width (CSW) and each coil loop having acoil outside width (COW) and coil inside width (CIW) such thatCOW=CIW+(2×CSW). wherein the coils have a coil outside length (COL),forming a coil assembly area (CAA) approximately equal to COW×COL andsaid coil assembly has a coil assembly thickness (CAT) in a directioncreating a coil assembly volume (CAV) approximately equal to the coilassembly area (CAA) times the coil assembly thickness (CAT) i.e.CAV≈CAT×COW×COL, wherein said assembly is formed with a plurality ofphases each formed in the manner of a first phase, each phase uniformlyand sequentially offset from adjacent phases and means for switchingcurrent successively between the phases thereby alternating the magneticfields within the coil assembly sequentially, said plurality of offsetphases substantially filling the coil inside width (CIW) of the firstphase, such that CIW=CSW×(#φ-1).

In alternative embodiment, the present invention includes a linear motorcomprising a DC magnetic field of alternating polarity arranged in alongitudinal axis, a coil assembly located substantially in a planeparallel to and immersed in the alternating field, said coil assemblycontaining individual coil loops of essentially rectangular shape havingend turn areas arranged parallel to said longitudinal axis of themagnetic field and coil side areas being perpendicular to saidlongitudinal axis of the magnetic field, further including a mountingbracket attached to one end turn area and a heat sink cap attached tothe end turn area opposite said mounting bracket.

Finally, in yet another alternative embodiment, the present inventionrelates to a linear motor comprising a DC magnetic field of alternatingpolarity arranged in a longitudinal axis forming a magnetic path, a coilassembly located substantially in a plane parallel to and immersed inthe alternating magnetic field, said coil assembly containing individualcoil loops of essentially rectangular shape having end turn areasarranged parallel to said longitudinal axis of the magnetic field andcoil side areas being perpendicular to said longitudinal axis of themagnetic field, wherein said coil assembly has a volume in the end turnareas through which an opening parallel to the longitudinal axis of themagnetic field is provided to accommodate cooling and support meansincluding a heat sink cap.

DESCRIPTIONS OF DRAWINGS

FIG. 1 is a front view of a single coil appropriate for a 4 phase coilassembly.

FIG. 1A is a side view, and

FIG. 1B is a top view.

FIG. 2 is a cross section of a coil assembly of the present invention,illustrating the two coil loops of a two phase coil assembly (end turnsnot shown).

FIG. 3 is an end view of a coil assembly of the present invention,illustrating the placement of a heat-sink cap attached to the end turnarea opposite a mounting bracket.

FIG. 4 is an end view of a coil assembly of the present invention, alsoillustrating the placement of a heat-sink cap, wherein said capsubstantially surrounds the end turn area.

FIG. 5 is yet another end view of a coil assembly of the presentinvention, wherein the end turn areas of the coil contain an openingextending into the volume of the coil loops, with heat-sink cap inplace.

FIG. 6 is a cross-sectional view of the magnet track plate separatingblocks and air gaps.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, FIG. 1A and 1B a basic view of coil loop 10 isillustrated. In addition, at 12 is what is defined herein as the coilside width (CSW), at 14 is the coil outside width (COW) and at 16 isshown the coil inside width (CIW) and at 18 a coil outside length (COL)is shown. In addition, it can be appreciated that notwithstanding thetwo-dimensional drawing provided for by FIG. 1, the coil illustratedtherein has a thickness in the direction perpendicular to the areabounded by COW and COL. Accordingly, and with reference to the abovedefinitions, the present invention, as previously noted above, firstincludes a linear motor comprising a DC magnetic field of alternatingpolarity arranged in a longitudinal axis, a coil assembly locatedsubstantially in a plane parallel to and immersed in the alternatingmagnetic field, said coil assembly containing individual coil loops ofessentially rectangular shape and having end turn areas arrangedparallel to said longitudinal axis of the magnetic field and coil sideareas being perpendicular to said longitudinal axis of the magneticfield with each coil side having a coil side width (CSW) and each coilloop having a coil outside width (COW) and coil inside width (CIW) suchthat COW=CIW+(2×CSW)., wherein the coils have a coil outside length(COL), forming a coil assembly area (CAA) approximately equal to COW×COLand said coil assembly has a coil assembly thickness (CAT) in adirection creating a coil assembly volume (CAV) approximately equal tothe coil assembly area (CAA) times the coil assembly thickness (CAT)i.e. CAV≈CAT×COW×COL, wherein said assembly is formed with a pluralityof phases each formed in the manner of the first phase, each phaseuniformly and sequentially offset from adjacent phases and means forswitching current successively between the phases thereby alternatingthe magnetic fields within the coil assembly sequentially, saidplurality of offset phases substantially and more preferably filling thecoil inside width (CIW) of the first phase, such that CIW=CSW×(#φ-1).

Those skilled in the art will recognize that the sequential relatedexcitation of the phases of the motor, as de3scribed above, result inproduction of force or linear movement of the coil assembly.

Having noted above, attention is next directed to FIG. 2, whichillustrates in cross-section two coils, 20 and 22, wherein said coilsrepresent individual phases designated as φ₁ and φ₂. As shown, the coilsides of the same phase do not abut and are spaced such that the coilside of the second coil loop 22 is positioned substantially parallel toand between the coil sides of the first coil loop 20.

Preferably, the coil loops are wound coils, and are would from bondablemagnet wire. In particular, the coils can be optimally wound via the useof a winding machine, e.g., automated winding equipment made availableby Airex Corporation, Dover, N.H. The coil end turns are also preferablyformed during winding, but those skilled in the art will recognized thatthe coils can optionally be wound straight, and bent after winding totheir final shape. Furthermore, a fiber cloth prepreg can be attached tothe external coil surfaces, for support and protection there of.

With respect to the above referenced embodiment, there are still otheradditional preferred modifications. For example, in a preferredconfiguration, the coil assembly contains a number of phases containinga number of coil loops wherein each phase had a minimum of one coilloop. Furthermore, the DC magnetic field of alternating polarity ispreferably comprised of a plurality of magnets aligned in a row forminga magnet plane having a longitudinal axis. In addition, the magneticcircuit completion means itself preferably comprises plates and a plateseparating rib, wherein the plate separating rib is a multiplicity ofblocks alternating with air opening running longitudinally along themagnet track. Such alternate air gaps improve heat dissipation as shownin FIG. 6.

Furthermore, with regards to specific preferred dimensions, when thelinear motor described above comprises a magnet track having a magnetpitch of 1.2 inches (the distance from a given point on one magnet tothe same point on the adjacent magnet) and a 3 phase (φ) coil assembly,employing 3 coil loops, the COW is about 1.6 inches, the CSW about 0.4inches, and a CIW of about 0.8 inches in dimension. The thickness in thedirection perpendicular to the coils sides is about 3/16 inches and thethickness perpendicular to the coil end turn areas is about 3/8 inches.

Turning next to FIG. 3, an end view of a linear motor is showncomprising a DC magnetic field formed by magnets 28 which are aligned ina row with alternating polarity arranged in a longitudinal axis. Alsoillustrated is the magnetic circuit completion means 29 and separatingrib 30, a coil assembly 31 located in a plane parallel to and immersedin the alternating magnetic field, said coil assembly containingindividual coil loops of essentially rectangular shape, having end turnareas 32 and 34 arranged parallel to said longitudinal axis of themagnet plane. Also shown is a mounting bracket 36 attached to one endturn area and a heat sink cap 38 attached to the end turn area 34positioned opposite to said bracket.

It can be appreciated that while heat sink cap 38 is shown attached tothe end turn area opposite to the mounting bracket, the heat sink capmay also be positioned to surround the ends of the coils. This is shownmore clearly in FIG. 4, wherein the heat sink cap 40 is specificallyillustrated as surrounding the ends of the coils loops. Additionally,with respect to the embodiment illustrated in FIGS. 3 and 4, it is to benoted that the heat sink cap preferably comprises a metallic material,such an aluminum.

Furthermore, and without being bound by any particular theory, inoperation, the placement of the heat sink cap as shown is believed toimprove heat dissipation to the extent that the cap uniformlydistributes any uneven heat generated. This may particularly be the caseat slow speeds or in stationary holding position, wherein one coil maybuild-up heat at a far greater rate than its neighbor.

Furthermore, it can be appreciated that heat sink fins may be optionallyadded to the heat sink cap to further enhance the ability of the cap todissipate heat build-up. Such fins, taking various forms, preferablyextend in the direction of coil travel thus maximizing air and heattransfer when moving quickly.

It is also to be noted that in addition to the advantages supplied bythe heat sink cap, noted above, the cap itself has been found to act asa stiffening structure to minimize uneven magnetic as well as inertialforces across the entire coil assembly. This strengthening is especiallyimportant when the motor is operating at very high temperature or atvery high power levels and/or speed.

Attention is next directed to FIG. 5, which illustrates that aspect ofthe present invention wherein the end turn areas of the coil contain anopening extending into the volume of the coil loops. That is, the endturn areas 42 and 44 each respectively contain an opening 46 and 48inside the volume of said coil assembly. The provision of said openings,it can be appreciated, provides additional surface area to the coilwhich in operation thereof, allows for more efficient heat dissipation.Furthermore, said opening can be optionally filled with a structuralsupport and/or heat conducting material, such as a brass rod, solder,alumina, lead wire, or the heat sink cap, which was described earlier.

Finally, and with reference to FIG. 5 for illustration purposes, thelinear motor of the present invention can preferably include at 50 aplurality of magnets aligned in a row forming a magnet plane having alongitudinal axis, a magnetic circuit completion means comprising aplate 52 and plate separating rib 54. Now, with reference to FIG. 6,which is a view taken along line A--A of FIG. 5, the plate separatingrib is again illustrated at 56 showing a multiplicity of blocks 58 withopenings 60. It can therefore be appreciated that such multiplicity ofblocks and openings provides yet additional opportunity for heat toescape from the linear motors of the designs and configurationsdescribed herein.

In sum, the foregoing disclosure and description of the invention areillustrative and explanatory thereof, and various changes in the size,shape and materials, as well as in the details of the illustrativeembodiments may be made without departing from the spirit of theinvention, all such changes being contemplated to fall within the scopeof the appended claims.

What is claimed is:
 1. A coil for a linear motor comprising:individualcoil loops of essentially rectangular shape and having end turn areasarranged parallel to a longitudinal axis of an alternating magneticfield and coil side areas being perpendicular to said longitudinal axisof the magnetic field with each coil side having a coil side width (CSW)and each coil loop having a coil outside width (COW) and coil insidewidth (CIW) such that COW=CIW+(2×CSW), wherein the coils have a coiloutside length (COL), forming a coil assembly area (CAA) approximatelyequal to COW×COL and said coil assembly has a coil assembly thickness(CAT) in a direction creating a coil assembly volume (CAV) approximatelyequal to the coil assembly area (CAA) times the coil assembly thickness(CAT), pursuant to the following equation: CAV≈CAT×COW×COL, wherein saidassembly is formed with a plurality of phases each formed in the mannerof the first phase, each phase uniformly and sequentially offset fromadjacent phases, said plurality of offset phases substantially fillingthe coil inside width (CIW) of the first phase, such thatCIW=CSW×(#φ-1), wherein the #φ represents the number of phases.
 2. Thecoil of claim 1, wherein said coil assembly contains a number of phasescontaining a number of coil loops wherein each phase has a minimum ofone coil loop.
 3. The coil of claim 1, wherein the end turn volume onboth sides of the coil assembly contain an opening in said volumesubstantially parallel to the longitudinal axis of the magnetic field.4. The coil of claim 3, wherein the opening in the volume is a groove orpenetration into the end turn areas.
 5. The coil of claim 3, wherein theopening into the volume is substantially surrounded by the wire formingthe coils.
 6. The coil of claim 3, wherein said opening containsmaterials providing structural support and heat conduction ordissipation comprising a brass rod, solder, alumina, lead wire or a heatsink cap.
 7. The coil of claim 1, wherein the end turn areas areparallel to the longitudinal axis of the magnetic field and containthermally conductive non-magnetic metallic members along thelongitudinal axis for structural support and heat conduction.
 8. Thecoil of claim 1, wherein a fiber-cloth prepreg is attached to the wireforming the assembly.
 9. The coil of claim 1, wherein said magneticfield of alternating polarity comprises a plurality of magnets alignedin a row forming a magnet plane having a longitudinal axis.
 10. The coilof claim 1, further comprising magnetic circuit completion meanscomprising plates and a plate separating rib.
 11. The coil of claim 8,wherein the plate separating rib is a multiplicity of blocks spacedlongitudinally along a magnet track, providing alternating support andair gaps.
 12. The coil of claim 1, wherein said coil comprises a 3 phase(φ) coil assembly, containing 3 coil loops, wherein the COW is about 1.6inches, the CSW about 0.4 inches, the CIW is about 0.8 inches indimension, and the thickness in the direction perpendicular to the coilssides is about 3/16 inches, and the thickness perpendicular to the coilend turn areas is about 3/8 inches when used with a magnet track havingmagnets spaced on a 1.2 inch pitch.